U.S. patent number 4,568,947 [Application Number 06/591,478] was granted by the patent office on 1986-02-04 for conductive fluid turbulence detection system.
This patent grant is currently assigned to Imaje S.A.. Invention is credited to Luc Regnault.
United States Patent |
4,568,947 |
Regnault |
February 4, 1986 |
Conductive fluid turbulence detection system
Abstract
A safety device for the conductive-fluid circulation system of
an ink-jet printer consists of a sensor and an associated
electronic circuit inserted between an ink-drop recovery trough and
a recirculating pump. The level of turbulence of the fluid flow
within a pipe segment of insulating material located between two
conductive pipe segments is determined by the sensor by measuring
the variation in conductivity in relation to variations in
cross-sectional area of fluid within the insulating pipe segment
and by delivering a control logic signal.
Inventors: |
Regnault; Luc (Bourg les
Valence, FR) |
Assignee: |
Imaje S.A. (Bourg les Valence,
FR)
|
Family
ID: |
9287414 |
Appl.
No.: |
06/591,478 |
Filed: |
March 20, 1984 |
Foreign Application Priority Data
|
|
|
|
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Mar 25, 1983 [FR] |
|
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83 05297 |
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Current U.S.
Class: |
347/6; 340/606;
340/611; 347/89; 73/861.08 |
Current CPC
Class: |
B41J
2/125 (20130101); G01N 27/10 (20130101); B41J
2/18 (20130101) |
Current International
Class: |
B41J
2/125 (20060101); B41J 2/18 (20060101); G01N
27/10 (20060101); G01N 27/06 (20060101); G01D
015/18 (); G01F 001/56 (); G08B 021/00 () |
Field of
Search: |
;346/75,14R ;73/861.08
;340/603,606,611 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goldberg; E. A.
Assistant Examiner: Preston; Gerald E.
Attorney, Agent or Firm: Plottel; Roland
Claims
What is claimed is:
1. A safety device for determining the condition of flow of a
conductive fluid within a conduit of a circulating system,
comprising: sensor means interposed within said conduit being in
fluid communication therewith so that said fluid will flow through
said sensor means, said sensor means including a pipe segment of
insulating material, and first and second conductive means coupled
on opposite sides of said insulating pipe segment so that said
fluid flows through said first conductive means, said insulating
pipe segment and said second conductive means; detecting means
connected to said sensor producing an electrical signal for
measuring variations in conductivity of said fluid therein
determined by variations in cross-sectional area of said fluid to
thereby determine the level of turbulence of said fluid within said
sensor; and indicator means connected with said detecting means for
indicating relative level of turbulence of said fluid.
2. The safety device according to claim 1 wherein said detecting
means comprises an electronic circuit connected between said first
and second conductive means, said electronic circuit including
means for measuring said variations of the electrical signal
between said first and second conductive means.
3. The safety device according to claim 2 wherein said signal is in
the form of a voltage representing a relative condition of
conductivity at a point in time as a function of the
cross-sectional area of the fluid within said insulating segment of
said sensor.
4. The safety device according to claims 2 or 3 wherein said first
and second conductive means comprise a conductive pipe segment
coupled at one of its ends to said conduit and at its other end to
said insulating segment.
5. The safety device according to claim 4 wherein said electronic
circuit comprises first, second, third and fourth subassemblies,
serially connected, said first subassembly comprising amplifier
means for generating said voltage and for reducing the impedance
applied to the input of said circuit; said second subassembly
comprising bandpass filter means for filtering the signal delivered
by said first subassembly; said third subassembly comprising means
for delivering a signal having a direct-current component in
functional relationship with the signal delivered by said second
subassembly; and said fourth subassembly comprising means for
comparing the signal delivered by the third subassembly with a
variable-reference signal and for delivering an output logic signal
having an "0" level or a "1" level representing the level of
turbulence of the fluid within said sensor.
6. An ink-jet printer comprising an ink reservoir, a first
pressurizing pump, a device for forming a jet of calibrated drops,
a set of charging electrodes, and deflecting plates, a recovery
trough, a recirculating pump for recirculating ink from said
recovery trough to said ink reservoir, a safety device for
determining the condition of flow of the ink between said recovery
trough and said recirculating pump, said safety device comprising
sensor means through which said ink will flow between said recovery
trough and said recirculating pump, said sensor means including a
pipe segment of insulating material and first and second conductive
means coupled on opposite sides of said insulating pipe segment,
detecting means connected to said sensor producing an electrical
signal for measuring variations in conductivity of said ink to
thereby determine the level of turbulence of said fluid within said
sensor, and indicator means connected with said detecting means for
indicating relative level of turbulence of said ink, said
recirculating pump being capable of delivering a signal which can
be utilized as a safety device control signal.
7. The ink jet printer, according to claim 6 wherein said first
conductive means is formed by said recovery trough made of
conductive material, and wherein said second conductive means
comprises a conductive pipe segment coupled with said insulating
segment so as to be in fluid communication therewith.
8. The ink jet printer, according to claim 6 or 7 wherein the
variation in conductivity has a spectrum in which the components
vary within the range of 40 to 100 Hz when the recirculation pipe
is 2 mm in diameter and a vacuum is produced by the recirculation
pump.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a safety device used in systems for
circulating a conductive fluid, especially ink-jet recovery
circuits in continuous ink-jet printers.
2. Description of the Prior Art
A frequent problem lies in the need to check whether a flow of
conductive fluid split-up in the form of drops within a pipe of
small diameter is taking place under acceptable conditions which
are conducive to good operation of the installation or on the
contrary whether any irregularities have developed and justify
remedial measures.
A problem of this nature arises particularly in the field of
ink-jet printers. In fact, among the different ink-jet printing
techniques, a certain number are based on the use of a continuous
stream of ink drops from which part of the stream is withdrawn for
the purpose of printing characters. The other drops are recycled in
a special circuit known as a recirculation circuit. Now a key
function of this device is the so-called "dump" zone for collecting
the unused stream of drops to be recycled. Taking into account the
nature of the inks employed which are capable by definition of very
rapid drying and also taking into account the small cross-sectional
area of the collecting element, blockage may eventually occur.
Another potential danger lies in the possibility of failure of the
pumping means. In all cases there is a risk of overflow of ink
which would have a damaging effect on the installation. In order to
avoid the consequences which would result from an operational fault
condition of this type, it is a desirable objective to provide
means for detecting such a fault condition in order to take the
necessary steps without delay. And this is precisely the aim of the
present invention.
SUMMARY OF THE INVENTION
In accordance with the invention, a sensor is adapted to cooperate
with an electronic circuit in order to detect the appearance of a
fault condition in the circulation of a conductive fluid within a
pipe of small diameter. The sensor accordingly delivers a signal
which can serve to initate a sequence for ensuring correct
operation while meeting safety requirements, for example by
completely stopping the machine.
The invention is more specifically concerned with a safety device
applied to a system for circulating a conductive fluid of the type
comprising a pipe for delivering the fluid to a pump. The
distinctive feature of the invention lies in the fact that it
permits measurement of the level of turbulence within the pipe by
measuring variations in conductivity of the fluid arising from
variations in cross-sectional area of said fluid within a pipe
segment of predetermined length L and formed of insulating material
.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features of the invention will be more apparent upon
consideration of the following description and accompanying
drawings, wherein:
FIG. 1 is a schematic representation of a sensor which is intended
to cooperate with an electronic circuit in order to constitute a
safety device in accordance with the invention;
FIG. 2 shows one example of construction of an electronic circuit
of this type;
FIG. 3 is a schematic representation of a device for recirculation
of the ink stream in a continuous ink-jet printer.
DETAILED DESCRIPTION OF THE INVENTION
For the sake of enhanced clarity, the same elements are designated
by the same references in all the figures.
As stated earlier, the non-limitative example chosen for the
purpose of illustrating the invention relates to the circuit for
recirculating the ink stream not employed for printing, in an
ink-jet printer. The recovered ink stream is collected by a pipe
which cooperates with a pumping means as will be explained
hereinafter and returns the ink to the supply tank for subsequent
reuse. The pipe under consideration has a diameter of the order of
one millimeter and receives a stream of spaced drops having a
diameter which is from five to ten times smaller.
If the flow were perfect and non-turbulent, air would circulate at
the center of the tube and the ink entrained by friction would
circulate at the periphery. But the action of gravity, friction
forces, the substantial difference in viscosity between air and ink
as well as other parameters in fact produce turbulent flow.
The present Applicant has found by experiment that a characteristic
flow pattern corresponds to normal recirculation. In fact, the
cross-sectional area of ink as it flows within the pipe is very
irregular. For a given length of piping, there is therefore a
variation in conductivity, the frequency of which indicates the
quality of flow of fluid at this level. Experimentally, the present
Applicant has found, for example, that with a tube 2 mm in diameter
and a vacuum of approximately 200 millibars, the variation in
conductivity takes place with a spectrum having a large number of
components which vary between 40 and 100 Hz.
In accordance with the invention, a sensor 100 as illustrated
schematically in FIG. 1 is interposed in the recirculation pipe.
This sensor consists of a pipe segment made up of two conductive
elements 20 and 21 which delimit an insulating element 22 having a
length L which will hereinafter be designated as an insulating
segment. The conductive elements are connected to the remainder of
the insulating pipe 23 and 24 in a conventional manner. The
combination of the two conductive elements 20 and 21 and of the
insulating segment 22 constitutes a sensor 100 which is adapted to
cooperate with an electronic circuit 101 shown in FIG. 2. The
design function of said sensor as contemplated by the invention is
to measure the variations in conductivity of the fluid and the
frequency of such variations, the measurement being performed at
the level of said insulating segment 22. A comparison is then made
with a reference signal which makes it possible to obtain an output
logical signal having a level 0 to 1 which can be employed as the
control signal of a safety device.
One example of construction of an electronic circuit 101 of this
type is illustrated schematically in FIG. 2. This circuit
essentially consists of four elements or subassemblies A, B, C, D,
the functions of which are described hereunder.
These subassemblies are essentially as follows:
A: a generator for producing voltage which is a function of the
variations in conductivity of the fluid segment contained in the
insulating segment 22 of the sensor 100;
B: a bandpass filter for delivering a filtered signal;
C: a voltage-amplifying peak detector;
D: a comparator.
The first subassembly A comprises the sensor described earlier and
the variation in conductivity which occurs at the level of the
insulating segment 22 is indicated by the conventional
representation of a variable resistance (a). The conductive element
200 is connected to ground M. This variation in conductivity (a) is
converted to a variation in voltage by means of the load resistor
32. An amplifier 33 produces a substantial drop in the impedance
applied to its input 31. The signal 34 at the output of the
amplifier 33 has a voltage equal in value to that of the signal 31
and is filtered in subassembly B of the circuit 101 by means of a
bandpass filter constituted by the resistors R1 and R2 and the
capacitors C1 and C2, said bandpass filter being in turn followed
by an amplifier 35. The resultant filtered signal 36 is applied to
the input of subassembly C of the circuit 101 which performs the
function of peak detector and voltage amplifier. This circuit
element or subassembly C comprises three resistors R4, R5, R6, a
capacitor C3, a diode D1 and an amplifier 37. Said subassembly
generates a direct-current voltage 38 which is a function of the
peak values of the signal 36 and therefore of the rapid variations
in conductivity of the fluid which circulates within the insulating
segment 22. Subassembly D is a comparator composed of an operator
40, the function of which is to compare the signal 38 with an
adjustable reference signal 39 in order to deliver an output signal
S.
When the flow of fluid within the insulating segment 22 is
satisfactory, the entire safety device constituted by the
combination of sensor 100 and of circuit 101 generates a signal
having a logic level "1" at the output S. If the flow is either
zero or non-turbulent as a result of low vacuum within the pipe,
the output S of the device generates a signal having a logic level
"0". This signal S which is representative of the state of
turbulence of the fluid can serve as a control signal for a safety
device.
A safety device in accordance with the invention as applied to an
ink-jet printer is represented schematically in FIG. 3. A printer
of this type essentially comprises an ink reservoir 11 and a first
pump 12 for putting this ink under pressure. The ink is then
directed via a supply line (fe) to the device 13 for forming the
jet 14 consisting of a succession of calibrated ink drops. These
drops are charged electrostatically by means of charging electrodes
15 before passing between two deflecting plates 16 in order to be
deflected and directed to a substrate to be printed (not shown in
the drawings). The unused drops are collected by a recirculation
trough 17 and returned via a recirculation pipe (f2) to the ink
reservoir 11 by second pumping means such as a recirculating pump
19.
In accordance with the invention, a safety device 1 formed by the
combination of a sensor 100 and an associated electronic circuit
101 is interposed in the recirculation circuit (f2) between the
collecting trough 17 and the recirculating pump 19. The schematic
diagram shows the insulating segment 22 having a length L which is
rigidly fixed to the conductive elements 21 and 20 on each side of
said segment. The element 20 is connected to ground M and the
element 21 is connected to the input of the electronic circuit 101
comprising four circuit subassemblies A, B, C, D, the structure and
functions of which have been defined earlier. The ink used for the
formation of drops which are intended to be charged
electrostatically is conductive by nature. At the level of the
recovery pipe (f2) which connects the collecting trough 17 to the
pump 19, a turbulent flow must take place in order to ensure
correct operation. The level of optimum turbulence is known in the
case of each application as a function of the different parameters
which characterize the printer such as type of ink, size of drops,
dimension of piping, and so on. For example, in the case of a tube
2 mm in diameter and a vacuum of approximately 200 millibars, the
variation in conductivity takes place within a spectrum comprising
a large number of components ranging from 40 to 100 Hz. As has been
stated earlier, the safety device 1 has the function of performing
measurements in order to determine whether the level of turbulence
satisfies these criteria within the recirculation pipe (f2). Should
this be the case, the output signal S is at level 1; otherwise it
is at level 0. Arrangements can then be made to overcome this
operational fault and to prevent any danger of ink overflow.
In an alternative embodiment of the invention, the first conductive
portion of the sensor 100 is constituted by the ink-drop collecting
trough 17 itself. This is conducive to a response time of minimum
duration between the appearance of a fault condition and activation
of safety system circuits.
A safety device of this type serves to protect the integrity of
equipment and its environment. Indeed an overflow of unrecovered
ink to be recirculated has a damaging effect and must be avoided as
far as possible.
* * * * *